Thread cutting device for sewing machines

ABSTRACT

A thread cutting device for sewing machines comprises an exclusively cutting knife mounted for displacement behind the needle axis upon release of a driving impulse independent on the drive mechanism of the machine, a knife support and the knife being mounted beneath the feed plate and the knife being movable upwards through an opening in the feed plate against the presser foot behind the needle axis.

United States Patent [72] Inventor Roll Ake Claesson 56] References Cited Malsryd, Sweden UNITED STATES PATENTS l 21] P 865,715 3,136,276 6/1964 Miyake 112/252 [22] PM ($1969 3 215 106 l1/l965 B0110 112/252 Patented Au83l1971 [73] Assignee AB J. A. Peterson 8: Co. Primary Examiner-James R. Boler Malsryd, Sweden Attorney-Young & Thompson [32] Priority Oct. 14, 1968 33} Sweden [3 l [3823/1968 [54] a i giagg DEVICE FOR SEWING ABSTRACT: A thread cutting device for sewing machines 2 claims 2 Drawing g comprises an exclusively cutting knife mounted for displacement behind the needle axis upon release of a driving impulse [52] US. Cl 112/252 independent on the drive mechanism of the machine, a knife [5|] Int. Cl D05b 65/00 support and the knife being mounted beneath the feed plate [50] Field of Search 112/252, and the knife being movable upwards through an opening in 129, 130 the feed plate against the presser foot behind the needle axis.

PATENTED was] um FIGJ INVENTOR.

. ROLF 4K5 CLAsso- 'rnREAn CUTTING DEVICE FOR SEWING MACHINES This invention relates to a thread cutting device for sewing machines comprising an exclusively cutting knife mounted for displacement behind the needle axis upon release of a driving impulse independent of the drive mechanism of the machine.

Devices of this kind are known which consist of a support for a knife mounted above the feed plate and behind the presser foot, which knife can be moved by means of a pneumatic or electric driving mechanism towards and against the feed plate for cutting the thread thereon.

Such known devices imply a certain danger because the operator can easily cut his finger. The knife can further easily form an obstacle to the feeding of the work during sewing. The lifting of the presser foot, which is normally coincident with the cutting of the thread, must be effected by hand and thereby brings the operator's fingers into dangerous proximity of the knife just when it becomes operative.

Other more complicated devices for separate or common cutting of the upper and under thread in a sewing machine are known which, however, imply important changes of the construction of the machine, and which cannot be mounted on existing standard machines. h

The invention concerns a device which brings an essential reduction of the danger of accidents which does not hinder the feeding of the work on the machine and which produces an automatic lifting of the presser foot. The device according to the present invention can further easily be mounted on existing machines. I

I These purposes are attained according to the present invention by the fact that a knife support and the knife are mounted V beneath the feed plate and are movable upwards through an opening in the feed plate to cooperate with the presser foot behind the needle axis. The presser foot is preferably provided wards to its lifted position normal for the beginning of a new seam, the presser foot being maintained in said lifted position by a known catch. I

An embodiment of the invention will be described hereinafter with reference to the accompanying drawing, FIG. I is an elevational section through the feedplate with the presser foot and the knife in position for sewing work. FIG. 2 shows the device in the position for cutting the thread.

In the drawing, 1 shows the presser foot which is mounted for limited rotation on a support 2 on the lower end of a presser bar 3 which in a known manner is displaceable upwards against spring action and which can be kept in its lifted position illustrated in FIG. 2 by a catch, not shown. The needle 4 is equally in a known manner mounted on the lower end of a needle bar 5. The presser foot normally rests against a feed plate 6 beneath which known feed and shuttle mechanisms are shown of which only the shuttle is diagrammatically shown at 7.

The presser foot 1 of the illustrated embodiment has an extension 8 projecting rearwards, i.e. in the feed direction (to the left in FIGS. 1 and 2) and presenting an under surface which .is retracted relative to the pressure surface of the presser foot I. A bracket 9 mounted on the machine frame piston rod 1l any appropriate hydraulic, electric or mechanical driving means can be used for the knife dependent on the power sources available in each special case.

When aseam is achieved, a few further stitches are made and the work is pulled rearwards so'thatits rear edge moves past the opening 14 in the feed plate 6 whereupon a drive impulse is fed into the drive means 10,11 whereby the angle iron 12 while sliding against the sliding list 15 and the knife 13 are moved upwards through the opening 14 against the underside of the extension 8 ofthe presser foot 1. The knife thereby lifts the presser foot 1 from the sewing position shown in FIG. 1 to the lifted position shown in FIG. 2. The knife 13 can also be arranged to maintain the presser foot in its lifted position until new material has been inserted under the presser foot. The advantage gained by providing the extension 8 with an under surface which is a little retracted relative to the pressure surface of the presser footl is that minor inequalities produced into the under surface of the extension by the knife do not impede the even feed of the work.

Dependent on the type of driving means used and on the driving medium, the driving impulses can consist of contacts or valves which are operated by the operator with the hand, the knee or the foot, e.g. of an extra contact operated by the ordinary regulating pedal when swung backwards (with the heel downwards). The releasing of the driving impulse for the knife can also be effected automatically dependent on the other functions of the machine or on the position of the work, e.g. by built-in contacts or valves, photocells, fluidistors etc.

The invention is not either in other aspects limited to the embodiment described and illustrated in the drawing. While the knife has been described as a member mounted for parallel motion, it can also be formed of the angularly bent end of a rockatable lever which can be operated directly or indirectly byany driving means, e.g. by a horizontal electromagnet mounted under the feed plate which actions the knife lever by means of a bellcrank lever, a cam or the like. The device according to the invention can thus very easily be adapted to the space available beneath the feed plate in any sewing machine.

What I claim isi I 1. In a sewing machine having a feed plate for supporting thereon material to. be sewed, a presser foot for pressing said material against said feed plate, the presser foot having a rearwardly extending portion that has an under surface that is stepped upward above that portion of the presser foot that engages said material, and a needle for sewing the thread through said material; the improvement in which said feed plate has a narrow opening therethrough disposed rearwardly of the axis of said needle and beneath said under surface of said presser foot, and a thread cutter mounted on the sewing machine and movable upwardly and downwardly through said opening into and out of engagement with said under surface to 

1. In a sewing machine having a feed plate for supporting thereon material to be sewed, a presser foot for pressing said material against said feed plate, the presser foot having a rearwardly extending portion that has an under surface that is stepped upward above that portion of the presser foot that engages said material, and a needle for sewing the thread through said material; the improvement in which said feed plate has a narrow opening therethrough disposed rearwardly of the axis of said needle and beneath said under surface of said presser foot, and a thread cutter mounted on the sewing machine and movable upwardly and downwardly through said opening into and out of engagement with said under surface to sever the thread against said under surface.
 2. Apparatus as claimed in claim 1, said presser foot being mounted for vertical movement with said cutter upon upward movement of saiD cutter into engagement with said under surface. 